Is the Grizzly Cable just a simple Ethernet/Cat5 cable?

No. A Cat5 cable is typically un-shielded, a balanced signal and uses different wiring for a computer vs a CNC control. The Grizzly Cable is shielded, with an ultra low capacitance, uses un-balanced signals and wired for RS232 signals. CAT5 cables are unreliable, able to pick up RF noise very easily and have limitations regarding baud rate when running beyond RS232 specificiations. ... more